1. Field of the Invention
The present invention relates to an apparatus and method for processing partitioned image data obtained by partitioning image data.
2. Description of the Related Art
A control apparatus for performing copying by controlling a scanner and printer is equipped with an image processing apparatus for converting image data read by the scanner into image data suitable for printing. Generally, a buffer for holding several lines of image data to be processed is provided as a structural element of the image processing apparatus. However, since an increase in image size is accompanied by an increase in line size as well, the above-mentioned method requires that the image processing apparatus be made over whenever the size of an image to be processed increases.
In order to deal with this, U.S. Pat. No. 6,950,559 discloses a method of partitioning image data, which is to undergo processing, into prescribed units (referred to as “band units” below) in the sub-scan direction, performing a scan conversion in units in which the data has been partitioned and then transmitting the resultant data to a subordinate image processing unit, which is a subsequent stage. This method is referred to as a cross-band method. By using the cross-band method, it is possible to execute processing of image data of any size using a buffer of limited size without dependence upon line size.
A problem which arises when an image is read is that owing to a variation in the characteristics of the reading sensor, the brightness level of the read data differs depending upon the sensor. To deal with this problem, a method known in the art is to accommodate for individual differences between sensors by applying an output-level correction conforming to each individual sensor and so arrange it that an image quality having a uniform brightness level is obtained. Image processing for carrying out such a level correction is referred to as a “shading correction”.
Filter processing, which is one form of image processing, makes reference to pixel values neighboring a pixel to be processed and performs a specific computation based upon these values to thereby calculate a processing result. Since neighboring pixels do not exist at the edge portions of image data, filter processing cannot be applied as is to these edge portions. However, a method that makes filter processing possible by appending dummy data to the periphery of the image-data edge is known. The dummy data appended for this purpose is referred to as “margin data” below. With the cross-band method, filter processing is implemented by appending the necessary margin data in band units. In general, the order in which the shading correction and filter processing are executed is such that the shading correction precedes the filter processing.
If it is attempted to apply the correction before the scan conversion when correction processing such as the shading correction is performed with the cross-band method, a line buffer conforming to the line size of the image is required and, hence, the advantage of the cross-band method is halved. Accordingly, it is desirable that the shading correction be applied to band data that prevails after the scan conversion. However, since margin data has been appended to the band data, the values of the margin data change from what is intended when the shading correction is applied to the margin data, and this has a deleterious effect upon the subsequent filter processing, etc.
Further, in the conventional method of setting margin data, the values of the margin data are fixed at white and margin size lacks flexibility as well. There is usually no problem when the values of the margin data are white. However, if the values of the margin data are white when an original such as film is read, there is the possibility that the image quality of the result of image processing that refers to the margin data will not be what is desired. Further, although a large margin size can be set in the main-scan direction, almost no margin can be appended in the sub-scan direction.